> thickness # plys parallel perpendicular > 0.125" 3 15.17 5.544
... but after looking at these numbers, I think I just started an argument with myself. I had to wonder what's wrong with vertical, since that would be "parallel to the grain", and by far the strongest. The point of these faces is to keep the spar caps from separating (the verticals would take handle the buckling). given the 3x strength difference from vertical to horizontal, I'd have to vote for vertical grain, like the plans show. So I went to talk to my stress analyst buddy, a guy who does aircraft and space vehicle stress analysis every day for a living, and then goes home and designs his own aircraft just for kicks. He's knows this stuff inside and out. He says those webs are shear webs, and therefore should be at a 45 degree angle if you want the ultimate strength of the spar system. (like a truss). He says the verticals are there to break up the plywood into manageable shear panels. He votes for 45 degrees to the spar, and after that vertical, but horizontal doesn't look so good to me OR him... Mark Langford, Huntsville, AL N56ML at hiwaay.net see KR2S project N56ML at http://home.hiwaay.net/~langford
